Operating system (OS) virtualisation and processor utilization thresholds for minimizing power consumption in mobile phones

ABSTRACT

A mobile phone that uses OS virtualization for minimizing power consumption in mobile phones is provided. Apparatus and methods may involve conserving processor power in a mobile phone according to the invention may include the following steps. A first step may be awakening a first processing core from a low power state in response to a first operating system (OS) thread. A following step may include processing the first OS thread using the first processing core. A next step may include determining whether utilization of the first processing core over a first time period has exceeded a predetermined threshold. The method may also include awakening a second processing core from a low power consumption state if utilization of the first processing core over a first time period has exceeded a predetermined threshold.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/205,012, filed on Sep. 5, 2008, which is hereby incorporated byreference herein in its entirety.

FIELD OF TECHNOLOGY

This invention relates to techniques used to minimize power consumptionin a mobile phone. More particularly this invention relates to reducingidle time power consumption in a mobile phone.

BACKGROUND OF THE INVENTION

In a mobile phone, it is important to preserve power as much as possibleto maximize battery life. To preserve power, each operating system(“OS”) resident in the mobile phone looks for idle time when there is noprocessing to be done and attempts to put its associated hardware to“sleep”—i.e., to inactivate the hardware to the extent possible, so thatthe OS consumes less or no power during that idle time.

OSes in a mobile phone typically control the application stack, themodem, the Wi-Fi, the Bluetooth, the Mobile TV, just to name a selectedportion of the applications controlled by OSes in a cell phone. Duringidle times, such OSes typically perform periodic tasks. Before goingidle—“to sleep”—the OSes schedule themselves to wake up for theseperiodic tasks. These periodic tasks may include, for example, the modemstack checking the paging channel for incoming calls and the userinterface (“UI”) OS checking the battery status and updating the clockon the display. Often these tasks are dependent on waking another of theOSes—for example the UI OS may need to wake up the modem OS to get thecurrent mobile signal strength to update the cell phone display.

Under normal usage, these regular wake-up events consume a majority of amobile phone's battery. A large proportion of that power consumptionhappens during the actual wake-up and going back to sleep mechanism foreach of the processing cores associated with each OS.

Accordingly, any mechanism that can be implemented to reduce this powerconsumption is desirable.

SUMMARY OF THE INVENTION

A system and/or method for reducing power consumption of a mobile phone,substantially as shown in and/or described in connection with at leastone of the figures, as set forth more completely in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will be apparent uponconsideration of the following detailed description, taken inconjunction with the accompanying drawings, in which like referencecharacters refer to like parts throughout, and in which:

FIG. 1 shows a schematic diagram of a conventional cell phone;

FIG. 2 shows another schematic diagram of a conventional cell phone;

FIG. 3 shows a shows a schematic version of the conventional operationof a hypervisor;

FIG. 4 shows a schematic diagram of a cell phone that may benefit fromhypervisor technology according to the invention;

FIG. 5 shows a diagram of the power consumption over time for aconventional processor core;

FIG. 6 shows a diagram of the power consumption over time for aprocessor core according to the invention;

FIG. 7 shows an illustrative flow diagram of a method according to theinvention;

FIG. 8 shows a schematic diagram of an example of different thresholdsof processing power consumption;

FIGS. 9A and 9B represent power consumption over time of a first andsecond processor; and

FIG. 10 shows a schematic diagram of an illustrative single ormulti-chip module of this invention in a data processing system.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the various embodiments, reference ismade to the accompanying drawings, which form a part hereof, and inwhich is shown by way of illustration various embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural and functional modificationsmay be made without departing from the scope and spirit of the presentinvention.

Increasingly mobile phones have more than one processing core—i.e., thehardware typically referred to as the central processing unit (“CPU”).Particularly, “smart-phones” that contain fully-featured user interface(“UI”) operating systems (“OS”) such as Windows Mobile™, Symbian™ orLinux™, implement multiple processing cores. A typical smart-phone willhave one silicon-chip based hardware core running the UI OS, anothercore running the modem stack OS and possibly other cores running otherperipheral software stacks such as GPS, WiFi, Mobile TV, multimedia,Bluetooth, etc. For the purposes of this application the term stack maybe defined as a software component resident in a device memory thatpreferably relates to a particular software application. Such exemplarysoftware applications that may be supported by their own dedicated stackinclude a user interface application or a mobile communications dataprocessing stack. A stack can contain its own dedicated OS.

The majority of functions performed on a mobile phone only use a smallfraction of the total processing capability of the cores, but it isnecessary to have a large amount of processing capability to support asmall number of computation intensive functions that are required in thephone. Examples of these may include high speed data transfer andhandling of complex video processing. For most phones it is necessary tohave a greater amount of UI processing than modem processing to providea good user experience associated with the UI tasks. Therefore it isnormal to have one core dedicated to the UI stack that runs much fasterand consumes much more power than the other cores.

Currently the low processor intensive tasks such as making a voice callor listening to a MP3 will generally run software from both the modemand OS stacks to provide the service and will therefore have bothprocessing cores awake and consuming power albeit they may be able tosleep for small periods during that processing.

The present invention is based around OS virtualization or “hypervisor”technology. A hypervisor is software that runs (as an operating systemcontrol program) directly on a given hardware platform. Consequently,‘guest’ OS(es) then run at a second level above the hardware whereby allaccess to the hardware is controlled by the hypervisor software.Specifically, the details of the hardware are effectively abstracted bythe hypervisor code and each OS runs in a virtual machine. In this wayit is possible to allow two or more OSes to run on a single processingcore with each perceiving that it is the only OS running on thatprocessing core. In alternative embodiments of the invention, suitablesoftware which may work instead of a hypervisor may also be implementedto provide OS virtualization. Nevertheless, for the sake of simplicity,the application describes the invention in terms of hypervisorutilization. But, it should be understood that the invention is notlimited only to hypervisor technology to virtualize an OS.

With a hypervisor, the OSes run in a virtual environment whereby accessto memory, processor scheduling, etc. are all handled by the hypervisor.In such an environment, it is relatively less complex to change theunderlying hardware without having to change the OS code. One suchconventional application of hypervisors that adapt the OS/processingcore relationship without changing the OS is to allow a single OS to runon multiple processing cores (which may all share access to a singlememory system). Each core runs an instance of the hypervisor and therespective hypervisor instances communicate with each other to schedulethe OS threads across the processing cores—each thread of the OSoblivious to the fact that the threads are not all running on a singleprocessor. Importantly, this process of running an OS over a hypervisorin a virtual machine can be done for 3rd party OSes such as WindowsMobile and Linux without having to make changes within the 3rd partysoftware.

One embodiment of this invention may be implemented in a mobile phoneApplication-Specific Integrated Circuit (“ASIC”) containing two ARM™processing cores—e.g., one core for the modem stack and one core for theUI OS. Each core has the same access to all the hardware peripherals (asin the existing BCM2152, BCM2153 and BCM21551 manufactured by BroadcomCorporation™, of Irvine, Calif.). If each of the OSes are ported to workover a hypervisor that runs on each processing core then the OSesfunction as before. If one of the cores—e.g., the lowest power one—ischosen as a periodic wake-up chip, the respective hypervisors can beconfigured to run the periodic wake-up threads on that core only.Consequently, only one processing core needs to be powered up duringidle periods. Thus, as long as the software instructs the UI OS wake-upsto be concurrent with modem OS wake-ups, this approximately halves thepower consumption of wake-up and sleep functionality because only onecore is being awakened rather than two cores. The power saving isrealized because the power consumption associated with the waking andputting to sleep of the second core is eliminated.

A further advantage to this system is that the non-waking core cansafely be put in a very deep sleep—i.e., a relatively very low powerconsumption state—possibly saving more power even if there is anassociated wake-up latency—i.e., the amount of time it takes for a coreto transition from a sleep state to an operational state—as the othercore can handle processing until it is awake. Also any inter-OScommunication required during the periodic wake-ups may have a lowerlatency as the threads will be running on the same awake core—thusminimizing the duration of the wake-up and reducing power consumption.

Systems and methods according to the invention could be implemented, forexample, on the BCM2152, BCM2153 and BCM21551 all of which have a modemstack core and a UI OS core and all of which have equal access to memoryand peripherals from both cores.

Existing hypervisor technology works with many conventional UI OSes andmodem OSes and allows for them both to run on a single processor. Thisallows for threads from different OSes to be inter-twined in priorityfor scheduling so the hypervisor task scheduler can work incollaboration with existing sleep control code to implement thisinvention.

In summary, systems and methods according to the invention have providedmobile phone power saving without the need for major changes in any ofthe existing software or in the delivered functionality of 3rd partyOSes. Furthermore, systems and methods according to the inventionpreferably do not require changes to any known hardware to save power.

A more specific statement of the invention may be as follows.Conventional hypervisor technology allows a single core to be designatedfor more than one application stack, so, theoretically, a device mayrequire fewer processing cores than the same device without thehypervisor. Nevertheless, many devices continue to maintain a dedicatedcore processor for each individual application stack. In these devices,the invention provides systems and methods, which may includeappropriately configured hypervisors, that select certain categories oftasks from each of a number of multiple application stacks and route thetasks in these categories to a predetermined processor core. Suchselected task categories may include periodic tasks which are performedwhen the processors are in an idle state. By routing some or allperiodic tasks from a number of different applications to a singleprocessor, the invention avoids redundant power-cycling of processorcores.

The scope of the invention also extends to less than a full hypervisortakeover of the OSes and implementation of each of the OSes in a virtualmachine. For example, only the code in the OS threads that areperiodically woken up can be put on one core by shifting the codeassociated with these threads into one OS.

There are other processing cores in many phones which could also be madeto work over the hypervisor so their respective wake-up threads can runon the one core. One example of another processing core is the GPSdevice which, in certain implementations, has periodic communicationwith the modem OS which would be optimized in terms of power consumptionusing this invention.

This invention may be yet further extended to other embedded devicesthat run off of a battery—an example may be a device with a WiFi corethat has to wake to receive messages and another core that maintains auser display.

FIG. 1 shows a schematic diagram of a cell phone 150 that could be usedfor systems and methods according to the invention. Cell phone 150preferably include components HSDPA Transmitter DAC 102, HSDPA RFControl 104, HSDPA RX ADC 106, EDGE¹ TX DAC 108, EDGE RF Control 110,and EDG RX ADC/DigiRF 112 (each of which forms a portion the hardwarefor converting the digital signal from the modem to an analogue RFsignal for the antenna and vice-versa). WCDMA²/HSDPA RF subsystem 114,GSM/GPRS/EDGE subsystem 116, and antenna 118 are for establishing aconnection between the phone and the cell. ¹ Enhanced Data rates forGlobal Evolution—EDGE uses the same spectrum allocated for GSM900,GSM1800 and GSM1900 operation. Instead of employing GMSK (GaussianMinimum Shift Keying) EDGE uses 8PSK (8 Phase Shift Keying) producing a3-bit word for every change in carrier phase. This effectively triplesthe data rate offered by GSM. The use of EDGE enables GSM to increasethe data rates that can be offered to users of the GSM spectrum.²WCDMA—Wideband Code Division Multiple Access—An ITU (InternationalTelecommunications Union) standard derived from CDMA (Code DivisionMultiple Access) technology.

Applications Stack Processor 120, GSM/GPRS/EDGE/WCDMA/HSDPA Modem StackProcessor 122, WCDMA/HSDPA Modem 124 and GSM/GPRS/EDGE Modem DSP 126 arethe core processing logic and further contain relevant mobile phonecommunications protocols.

Finally, components TV 128, IR (Infrared) 130, UART 132 (UniversalAsynchronous Receiver/Transmitter—i.e., hardware that translates databetween parallel and serial interfaces) external memory control 134,(U)SIM³ 136, SDIO (Secure Digital Input/Output (SDIO) is a standard fordevices that feature interchangeable memory options) 138, camera 140,LCD 142, GPIO/Keypad 144, USB interface 146, and audio 148 are all forconnections to phone peripherals. 32 kHz XTAL 152 (an oscillator thatuses a quartz crystal to generate a frequency) is coupled to PMU (PowerManagement Unit) which is, in turn, coupled to CLK (Clock) 156 and I2CBus 158. Furthermore, battery 160, charger 162, backlight 164, andvibrator 168 (or other tactile feedback) are shown schematically forillustration. ³ USIM—UMTS Subscriber Identity Module Usually referred toas a SIM card, the USIM (UMTS Subscriber Identity Module) is the usersubscription to the UMTS mobile network. The USIM contains relevantinformation that enables access onto the subscribed operator's network.

Applications stack processor 120 and modem control processor 122 eachrepresent a separate core processor. In one set of circumstances,processor 120 may receive a user inputted number and then receive a sendcommand. Baseband processor may then transfer the inputted number tomodem processor 122 in order to make the cell phone call. Each processortypically has an OS residing in its one respective Random Access Memory(“RAM”). Each respective processor provides services such as memorymanagement, scheduling, etc. Accordingly, the phone shown schematicallyin FIG. 1 may provide a platform for implementation of softwareaccording to the invention as will be explained in more detail below.

FIG. 2 shows a schematic version of the conventional operation of a cellphone having two core processors 206 and 214, such as the cell phoneschematically depicted in FIG. 1. The cell phone in FIG. 2 typicallyprovides telecommunication operations as shown in 202 and otherapplications as shown at 210. As described in FIG. 1, the cell phoneincludes telecom stack 204 (alternatively referred to herein as a “modemstack”), to control the telecommunications operations, and applicationsstack 212 to control the other cell phone applications. Core processor206 handles the processing functions required by telecom stack 204.These processing functions typically require interaction with thetelecom peripherals 208. Core processor 214 handles the processingfunctions required by applications stack 212. These processing functionsrequire interaction with the peripherals such as the USB port, thecamera, etc. 216.

FIG. 3 shows a schematic version of the conventional operation of ahypervisor. FIG. 3 includes the telecom operations, as shown in 302, theother applications, as shown at 304, the telecom stack, the applicationsstack, and a security stack (shown together at 306), the hypervisor 308,a single CPU core processor 310, and the various peripherals at 312.

Thus, hypervisor 308 has allowed for the removal of one of the CPU coreprocessors. Accordingly, known hypervisor technology reduces bill ofmaterial for cell phones and may mitigate certain security concerns.

Thus, in certain conventional situations, hypervisors have been used toobviate the need for multiple processing cores.

Nevertheless, certain cell phone platforms which continue to usemultiple core processors may still benefit, according to the invention,from hypervisor technology. FIG. 4 shows a schematic diagram of a cellphone that may benefit from selectively-applied hypervisor technologyaccording to the invention.

Telecom stack 402 preferably may implement processing threads 1.1 404and 1.2 406. For the purposes of this application, processing threadsindicate the communication between the application stack and theprocessing cores regarding tasks to be performed by the processing coreson behalf of the application stacks. Applications stack 408 mayimplement processing threads 2.1 410 and 2.2 412.

In a method according to the invention, threads 1.1 and 2.1 may be idlethreads which are selected to run on core processor 418 whereas threads1.2 and 2.2 may be non-idle threads which are selected to run on theirown core processors, 418 and 420, respectively. A hypervisor instanceruns over a single processor core and communicates with that core.Accordingly, hypervisor 414 is configured to run thread 2.1 410 on core418. Hypervisor 414 preferably can run thread 2.1 410 on core 418because the code for thread 2.1 410 resides in RAM which bothhypervisors 414, 416 and cores 418, 420 have access to.

The selection of threads 1.1 and 2.1 may preferably be implemented inhypervisor 414, transparent to the operation of the application stacks408.

FIG. 5 shows the relative advantage of such an implementation. FIG. 5shows a diagram 500 of the power consumption over time for aconventional processor core. In area 502, a first amount of power isconsumed when the core is waking up. For the purposes of thisapplication, the power consumed by “waking up” a processor may includethe power consumed by turning ON the processor, activating the memoryassociated with the processor, ramping up the processor clock (when theclock turns ON, it also takes time for the clock to settle) and otherpower consuming tasks associated with bringing a processor up to speed.Area 504 shows that, even after the core has reached a level at which itcan operate, an additional amount of power is consumed prior to the corebeing fully operational. Area 506 shows the power consumed when the coreis awake and fully functional.

Area 508 shows that when the core begins to return to sleep, the corecontinues to consume power at a high level even though it no longeroperates at a level of being awake. For the purposes of thisapplication, the power consumed by putting a processor “to sleep” mayinclude the power consumed waiting for the memory to stop drawingcurrent, the power consumed waiting for the clock to clear a hysteresisperiod, and the power consumed by the processor itself when it checks tomake sure the processor has no tasks remaining, just to name a fewexemplary power-consuming tasks performed by the processor when going tosleep. Finally, area 510 shows the power consumed when the core isreturning to a sleep state.

It should be noted that the area (which represents total powerconsumption) under the entire power consumption curve, or somesubstantially similar curve, shown in FIG. 5 is required for eachprocessor that needs to be awakened. Accordingly, a relatively largeamount of power is wasted when two processors are woken up because allthe unutilized power in areas 502, 504, 508, and 510 is duplicatedwithout deriving any operational benefit.

Whereas conventional devices perform the same tasks on multipleprocessors, methods according to the invention, on the other hand, use ahypervisor to selectively route certain tasks to a single processor. Inone embodiment of the invention such tasks may include tasks that areperiodically performed when the device is in a sleep state. Suchprocesses may be enabled at least through the implementation ofhypervisor technology using multiple processor cores. The hypervisortechnology preferably allows the direction of tasks to predeterminedprocessors at least for the purposes of reducing power consumption.

Additional advantages obtained by the invention include increased speedwhen running the periodic tasks. The increased speed reduces powerconsumed by reducing the time that the processor is operating. Theincreased speed is obtained by not requiring inter-processorcommunication during the periodic tasks because only a single processoris performing the periodic tasks during idle state and any inter-stackcommunication is handled directly on that processor.

FIG. 6 shows a diagram 600 of the power consumption over time for aprocessor core according to the invention. In area 602, the first amountof power consumed when the core is waking up is substantially equivalentto area 502. The amount of power consumed in area 604 the additionalamount of power is consumed prior to the core being operational issubstantially equivalent to area 504.

The true power savings, however, is evident in area 606. Area 606extends over a substantially longer time than area 506 because area 606represents the tasks that now are run from a single processor instead ofdual processors. Accordingly, the power consumed by the single processoris greater. However, there is no additional power consumed by thewake-up and going to sleep of a second processor.

Furthermore, inter-processor communication is reduced to zero for theperiodic tasks because a single processor is performing all the periodictasks. For example, the application stacks need to talk to one anotherfor certain periodic tasks. One such periodic task that requiresinteraction between the stacks is when the application stack requestsinformation regarding the signal strength from the modem stack. Theapplication stack may be requesting such information at least in orderto update the signal strength display on the cell phone.

It should be noted that area 608, when the core continues to consumepower at a high level even though it no longer operates at a level ofbeing awake, may be substantially the same as area 508. Finally, area610, the power consumed when the core is returning to a sleep state, maybe substantially the same as area 510.

In certain embodiments of the invention, when one of the processors isselected to be the processor that provides the idle time periodicprocessing, the other processor(s) may be redesigned such that it can beput in a relatively lower state of power consumption during itsrespective sleep period—i.e., the secondary, less-used, processor(s) maybe designed without a quick wake-up or a quick going to sleep time.Rather, the second processor can wake up more slowly and go to sleepmore slowly than the first processor in order to save additional power.For the time period when the second processor is waking up and going tosleep, its tasks may be covered by the first processor, as needed. Itshould be noted as well that the memory for a relatively slow coretypically uses less power than the memory for a relatively fast core.Accordingly, by moving all the low processing power tasks to the lowpower core, power used by external memory may be reduced.

Thus, it has been shown that, in a device that utilizes a hypervisor toallocate processing tasks between multiple processors, substantial powersavings can be realized by running certain periodic tasks through asingle processor.

It should be noted that while the description herein relates to cellphones, nevertheless, the systems and methods described relate readilyto other devices that include multiple application stacks and multipleprocessing cores. One such category of device that may include multipleprocessing cores and perform periodic tasks during an idle state is adigital camera, or a digital video camera.

Many digital cameras are battery-powered. Accordingly, power consumptionis an important factor in the design of such cameras. Furthermore, manydigital cameras consume a large amount of power when idle. It would beadvantageous, therefore, to implement systems and methods according tothe invention as described herein for multi-processing core digitalcameras and/or digital video cameras.

Other possible implementations of the invention may includemulti-processor digital audio players such as MP3 players—e.g., the iPodmanufactured by Apple Computer, Inc. of Cupertino, Calif., or othersuitable, portable electronic device.

FIG. 7 shows an illustrative flow diagram of a method according to theinvention. The flow diagram is preferably implemented on a mobile phonethat includes a hypervisor—alternatively referred to herein as a“hypervisor instance”—for each individual core (though the inventioncould also be implemented using a single hypervisor for multiple cores).Step 702 shows the phone in idle state. In certain embodiments of theinvention, the hypervisor has configured hardware so that preferably anywake-up signal routes to core I. In the preferred embodiment of theinvention, core I is the lowest power and lowest performance core.

When the user initiates performance of a function on the user's mobilephone, the phone transitions from idle mode and awakens core I. Step 704shows that core I processes the thread and sleeps in idle time.

The hypervisor preferably monitors the processor utilization over aprevious, preferably predetermined, time period. Step 706 shows that thehypervisor can query whether processor utilization of core I over apreceding amount of time has exceeded a threshold amount. The amount oftime for the preceding time period can be configurable for optimal powersaving/performance. It should be noted that, in order to increaseefficient core utilization even more, the hypervisor can preferablydynamically adjust core usage as needed because the hypervisor itselfcontrols thread scheduling and termination.

In alternative embodiments of the invention, the determinations may bemade using instantaneous measurements of processing usage instead of, orin combination with, determinations over a preceding time period.

If the processing exceeds a first configurable threshold as determinedin query 706 then the core I hypervisor instance will wake core IIstarting the core II hypervisor instance, as shown in step 710. If theprocessing power consumption is below the first configurable threshold,then the method may query whether the phone has returned to an idlestate, as shown in step 708.

If the phone has returned to an idle state, then the flow may loop backto step 702 and await the next core I awakening event. If the phone hasnot returned to an idle state, then the flow may loop back to where coreI continues to process as shown by the flow returning to the step shownin 704.

From step 710, the two hypervisor instances preferably communicate toschedule threads. Nevertheless, the modem threads may preferably be runon core I and UI threads run on core II to make inter-threadcommunications most efficient, as shown generally at step 712.

Step 714 shows that the hypervisors preferably continue to monitorutilization on each core and, if the total drops below a secondthreshold, the hypervisors, or other suitable software and/or hardware,can decide to route all new threads to core I and put core II back tosleep. In certain embodiments of the invention, the firstthreshold—i.e., the threshold required to awaken core II—corresponds tothe same per processor power consumption as the threshold required toput core II to sleep. Thus, a mobile phone according to the inventionmay typically query whether the processing power consumption is above orbelow a first threshold.

It should be noted, however, that the first threshold and the secondthreshold may be at different levels of processing power consumption.Accordingly, it may require a higher (or lower) level of processingpower consumption per processing core to awaken core II than it requiresto put core II to sleep. Such an embodiment may preferable prevent a“hunting” phenomenon whereby the phone is turning core II on and offrepeatedly when the phone processing power consumption hovers in thearea of the threshold.

In certain embodiments of the invention, each of the processors may beevaluated separately to determine the utilization of each of theprocessors. The evaluation of each of the processors may be combined toform a processor utilization index. The processor utilization index maybe used to determine whether to maintain one or both (or more) of theprocessors in an awakened state. In fact, any suitable combination ofthe utilization of each of the processors may be used to determine whichof the processors should be maintained in an awakened state.

FIG. 8 shows a schematic diagram of an example of different thresholdsof processing power consumption. The y-axis represents total processingpower consumption for a mobile phone or other suitable device, while thex-axis represents time.

In the embodiment schematically shown in FIG. 8, a user make a normalvoice call which takes the processing 802 from a very low level to astable level of processing below a first threshold 804. In this case allthe modem and UI threads will preferably be run on core I.

Then, if the user initiates a second application while still on thecall, such as opening the phone's address book, the processing mayexceed the first threshold 804 for operating only core I. (It should benoted that the utilization of core I should typically be maintainedbelow 100% utilization of core I so as to not affect performance.) CoreII is then awakened and the processing is then spread across core I andcore II.

In certain embodiments of the invention, if the usage were to drop belowthe first threshold 804, core II could then be put to sleep. In otherembodiments, a second threshold 806, the operation of which wasdescribed above, may be used in order to implement a level of hystereticoperation on the processing power consumption whereby core II will onlygo back to sleep after a relatively substantial drop in processing powerconsumption.

If the plurality of cores were to have an equal processing-to-powerconsumed ratio and no power was consumed waking up and going to sleep,then moving the threads around in the methods stated above would notsave any power because the threads would run across the two coresquicker and therefore they would sleep for longer. However, theplurality of cores typically do not have an equal processing-to-powerconsumed ratio and power is consumed waking up and going to sleep.Specifically, the higher performance a processing core is—i.e., thehigher the normal running speed of the core is—the more difficult thecore is to put into a low power mode—i.e., a sleep mode—and itswake-up/sleep latency gets longer.

This principle is illustrated in the schematic diagrams shown in FIGS.9A and 9B. FIG. 9A represents the power consumption of a first processorhaving a relatively lower power consumption and lower processing power.FIG. 9B shows the power consumption of a second processor having arelatively high power consumption and high processing power.

Areas 906 and 916 are the times during which useful processing is takingplace for each of the different processors, respectively. As would beexpected (albeit not shown)—the same thread running on core 1 will takelonger, and may require less power, to complete than when running oncore 2. Accordingly, there are some savings to be made using a slowerprocessor when the task may be accomplished in a longer period of time.

However, these power savings are not significant. Rather, the main powersaving according to the invention comes in the power consumed waking upand putting to sleep the processor during idle times when performing lowprocessing-intensive tasks. For example, areas 902 and 910, whichrepresent the power consumption of the processor in FIG. 9A when it isbeing awakened and put to sleep, are relatively much smaller (eventaking into account the greater processing power of the processor shownin FIG. 9B) than the power consumption areas 912 and 916, whichrepresent the power consumption of the processor in FIG. 9B when it isbeing awakened and put to sleep. In addition, the shape of the areas istypically more power friendly in the lower-power consuming cores than inthe higher power-consuming cores because of the sacrifices necessary toattain high processing speeds.

Thus, the power consumed waking up and going to sleep for the low powerprocessor is much smaller. Furthermore, by having only a single core (orsome number less than a maximum number of cores) do all the processing,the single core is awake longer and should be doing less wake-up andsleep transitions. Therefore, the total power consumed for substantiallyall low processor intensive tasks will be substantially lower on just asingle, preferably low processor power, core.

Areas 904 and 914 show that, even after the core has reached a level atwhich it can operate, an additional amount of power is consumed prior tothe core being fully operational. Areas 908 and 918 show that when thecore begins to return to sleep, the core temporarily continues toconsume power at a high level even though it no longer operates at alevel of being awake. During the time covered by areas 904/914 and908/918, the state of the core is being transitioned using softwarerunning on the core from sleep to running tasks and running tasks tosleep. By using only the low-power core when possible, the total powerconsumed during these areas should be lower than power consumed by thehigher power core or power consumed by a combination of both the highpower core and the low power core.

In some embodiments of the invention, one does not need to use a fullhypervisor (or multiple hypervisor instances) and run the OSes in avirtual machine to implement systems and methods according to theinvention. Instead, the code in the threads that use a low amount ofprocessing time could all be put on one core by simply shifting the codeall into one OS. Nevertheless, this would require relatively largercoding changes in the OS than the other method using one or morehypervisors as described above.

FIG. 10 shows a single or multi-chip module 1006 according to theinvention, which can be one or more integrated circuits, in anillustrative data processing system 1000 according to the invention.Data processing system 1000 may include one or more of the followingcomponents: peripheral devices 1002, I/O circuitry 1004, multipleprocessing cores 1008 and memory 1010.

These components are coupled together by a system bus or otherinterconnections 1012 and are populated on a circuit board 1016 which iscontained in an end-user system 1018. System 1000 is configured for usein a mobile phone according to the invention. While system 1000represents a generic embedded device with multiple processing coreswhich, according to the invention can use a hypervisor to wake a singleprocessor for idle tasks, nevertheless, it should be noted that system1000 is only exemplary, and that the true scope and spirit of theinvention should be indicated by the following claims.

Aspects of the invention have been described in terms of illustrativeembodiments thereof. A person having ordinary skill in the art willappreciate that numerous additional embodiments, modifications, andvariations may exist that remain within the scope and spirit of theappended claims. For example, one of ordinary skill in the art willappreciate that the steps illustrated in the figures may be performed inother than the recited order and that one or more steps illustrated maybe optional.

Thus, systems and methods for reducing power consumption in a mobilephone have been described. Persons skilled in the art will appreciatethat the present invention can be practiced by other than the describedembodiments, which are presented for purposes of illustration ratherthan of limitation, and the present invention is limited only by theclaims which follow.

What is claimed is:
 1. A mobile phone comprising: a plurality ofapplication stacks; a plurality of processor cores; and a plurality ofhypervisor instances, each of the hypervisor instances that correspondsto a single processor core; wherein: when total power consumption of theplurality of processor cores over a predetermined time period is below afirst threshold, a first hypervisor instance allocates tasks from eachof the application stacks to a first processor core; when powerconsumption of the plurality of processor cores over the predeterminedtime period is above the first threshold, the first hypervisor instancethat causes a second processor core to awaken and to run a secondhypervisor instance thereon, the second hypervisor instance forallocating selected tasks from the plurality of application stacks tothe second processor core; and the first processor core stops drawingcurrent following turn OFF relatively faster than the amount of timethat the second processor core stops drawing current following turn OFF.2. The mobile phone of claim 1, wherein the second hypervisor puts thesecond processor core into a lower power consumption state when thepower consumption of the plurality of processor cores is less than thefirst threshold.
 3. The mobile phone of claim 1, wherein the secondhypervisor puts the second processor core into a lower power consumptionstate when the power consumption of the plurality of processor cores isless than a second threshold.
 4. The mobile phone of claim 3, whereinthe first threshold represents a higher level of power consumption thanthe second threshold.
 5. The mobile phone of claim 1, wherein theplurality of application stacks comprise at least two stacks selectedfrom a software peripheral stack, a mobile TV stack, a modem stack, aWi-Fi stack, and a Bluetooth stack.
 6. The mobile phone of claim 1,wherein the first processor core comprises a turn-ON power consumptionthat that is less than the turn-ON power consumption of other processorcores of the plurality of processor cores.
 7. A method of conservingprocessor power in a mobile phone, the mobile phone comprising aplurality of processing cores, the method comprising: awakening a firstprocessing core from a low power state in response to a threadassociated with a first operating system (OS); processing the threadassociated with the first OS using the first processing core; processinga thread associated with a second OS using the first processing core;determining whether utilization of the first processing core over afirst time period has exceeded a first threshold; and if utilization ofthe first processing core over a first time period has exceeded thefirst threshold, awakening a second processing core from a low powerstate; wherein the first processing core stops drawing current followingturn OFF relatively faster than an amount of time that the secondprocessing core stops drawing current following turn OFF.
 8. The methodof claim 7, further comprising, if the utilization of the firstprocessing core over the first time period did not exceed the firstthreshold, determining whether the first processing core can be put intoa low power state.
 9. The method of claim 7, further comprising,following the awakening of the second processing core, scheduling aplurality of OS threads on each of the first processing core and thesecond processing core.
 10. The method of claim 7, further comprising:following the awakening of the second processing core, determiningwhether a collective utilization of the first processing core and thesecond processing core over a second predetermined time period hasdropped below the first threshold; and if the collective utilization hasdropped below the first threshold, placing the second processing core ina lower power state.
 11. The method of claim 7, further comprising:following the awakening of the second processing core, determiningwhether a collective utilization of the first processing core and thesecond processing core over a second predetermined time period hasdropped below a second threshold, the second threshold being a lowerprocessing utilization per core than the first threshold; and if thecollective utilization has dropped below the second threshold, thenplacing the second processing core in a lower power state.
 12. Anelectronic device comprising: a plurality of application stacks; aplurality of processor cores; and a hypervisor; wherein, when totalpower consumption of the plurality of processor cores over apredetermined time period is below a threshold level, the hypervisorallocates processing tasks from the plurality of application stacks to afirst processor core, and, when power consumption of the plurality ofprocessor cores over the predetermined time period is above thethreshold level, the hypervisor awakens a second processor core andallocates selected processing tasks from the plurality of applicationstacks to the second processor core; and wherein the first processorcore stops drawing current following turn OFF faster than an amount oftime that other processor cores of the plurality of processor coresstops drawing current following turn OFF.
 13. The electronic device ofclaim 12, wherein the hypervisor puts the second processor core to sleepwhen the power consumption of the plurality of processor cores is lessthan the first threshold.
 14. The electronic device of claim 12, whereinthe hypervisor puts the second processor core to sleep when the powerconsumption of the plurality of processor cores drops below a secondthreshold.
 15. The electronic device of claim 14, wherein the thresholdrepresents a higher level of power consumption than the secondthreshold.
 16. The electronic device of claim 12, wherein the firstprocessor core comprises a turn-ON power consumption that that isshorter than the turn-ON power consumption of the other cores of theplurality of processor cores.
 17. The electronic device of claim 12,further comprising a mobile phone.
 18. The electronic device of claim12, further comprising a digital camera.
 19. The electronic device ofclaim 12, further comprising a digital audio player.